Thermostat for cooking appliance or the like



April 16, 1957 A. H. FREEMAN 2,789,183

THERMOSTAT FOR cooxmc APPLIANCE OR THE LIKE Filed Aug. 6, 1954 a m /4 10 z a [7 van Z: or: A r/wr' H Freeman /"//5 Ator'ngg.

United States Patent THERMOSTAT FOR COOKING APPLIANCE OR THE LIKE Arthur H. Freeman, Allentown, Pa., assignor to General Electric Company, a corporation of New York Application August 6, 1954, Serial No. 448,235

15 Claims. (Cl. 200-138) My invention relates to heat responsive actuating devices and particularly to an improved thermostat.

The thermostat art, as highly developed as it is, constantly searches for simple, reliable, inexpensive constructlons, particularly those wherein the life of the contacts is maintained at a maximum. it will be readily understood, it is believed, that the effective life of the thermostat depends upon the life of the contacts. Two factors largely influence and shorten contact life: (1) unequal pressure between the contacts, which usually attends the adjustment of the temperature setting, and (2) slow parting of the contacts when the circuit is broken, which often results in arcing.

It is an object of my invention to provide an improved thermostat which is simple in construction, inexpensive to manufacture, reliable in use and which has a long life.

it is another object of this invention to provide an improved thermostat wherein the pressure between the contacts is constant for all temperature settings other than the off setting, and wherein the contacts part quickly when the circuit is broken.

The objects of my invention are accomplished in one form thereof by providing a thermostat having a novel switch arm and slide arrangement, and mounting both of the contacts on the switch arm.

Other objects and further details of that which I believe to be novel and my invention will be clear from the following description and claims taken with the accompanying drawing, wherein:

Fig. 1 is a front elevation view of the thermostat shown in an on temperature setting with the bimetal undeflected and the contacts closed.

Fig. 2 is a plan view of the thermostat.

Fig. 3 is a sectional view of the thermostat taken on line 3-3 of Fig. 1.

Fig. 4 is a view similar to Fig. 1, but showing the bimetal deflected and the contacts open.

Fig. 5 is a front elevation view of the thermostat in the off position.

Referring to the drawing, the thermostat is housed in the casing and is shown mounted in place in wall 12, which may form a part of an electrical cooking appliance or the like. As can best be seen in Figs. 2 and 3, wall 12 has a generally rectangular elongated opening 14 formed therein which communicates with small openings 16 at both of its ends.

Casing 16 generally comprises top wall 18, mounting panel 2%, and end legs 22. The casing 10 may be formed out of a piece of sheet material in a known manner. The ends of legs 22 have curved portions 23 which are adapted to be received in the small openings 16 when the casing is mounted on the wall. The casing 10 may be made of a flexible material and the legs 22 formed so that they have to be forced toward each other when being mounted on the wall, and after being placed in the position shown in the drawings, they will flex outwardly and press against the edges of the openings 16 and thereby maintain the casing in position. The casing is resiliently mounted by 2 ,789,183 Patented Apr. 16, 19,57

the provision of resilient members 24 about each leg 22. Members 24 may be coil springs having one end turn resting against the edges of an opening 16 and the other end turn resting against the lower face of top wall 18. Mounted in the foregoing manner, casing 10 has a certain amount of resilience and is flexibly mounted with relation to the wall 12.

Top wall 13 is generally rectangular and has two lanced legs formed therein. Leg 26 depends from the top wall and is L-shaped in cross-section, having a vertical section 28 and a horizontal section 30. The other leg 32 is straight in cross-section, depends vertically downwardly from the top wall and constitutes a stop, as will become apparent. Elongated bimetallic strip 34 is secured to the horizontal section 30 of the leg 26 in any conventional way, extends generally in a horizontal plane and has its free end 36 bent downwardly.

Panel 20 has a horizontal slot 38 shorter than the length of the panel formed parallel and adjacent to the lower edge of said mounting panel. Slide 46, of a novel configuration to be described, is mounted for horizontal movement in slot 38. The sliding mounting for slide 40 is accomplished by two double headed pins 42 which have central shaft portions which slide in the slot 38.

Slide 40 comprises a central planar portion 44 in which the double-headed pins are secured, an upwardly extending flat portion 46 and two depending spaced legs 48 having their adjacent lateral sides bent normal to the plane of the portions to form tabs 50. Tabs 50 receive an end of control lever 52 between them when the casing is mounted on the wall 12. The clearance between the lever and tabs facilitates manufacturing, for it permits considerable tolerance. Control lever 52 extends parallel to the wall 12 and is pivoted with relation thereto. In any particular setting, it might be more convenient for the lever to slide instead of pivot, in which case a sliding mounting may be employed. At its extremity it is provided with a control knob that is accessible from the exterior of wall 12 and associated with indicia calibrated to the thermostat. Neither the pivotal connection, the knob nor the calibrations have been illustrated, as they form no specific part of this invention. It is only necessary that there be a control lever having an end that is positioned between and cooperates with the tabs 50 of the slide 46. The detailed manner in which the lever and slide tabs cooperate will become apparent subsequently. In certain applications of my thermostat it might be desirable or convenient to eliminate the lever and tabs by providing a control lever integral with the slide 40; such a construction is contemplated by my invention.

The central portion 44 of the slide rigidly supports pin 54, which has a shaft portion 56 that extends laterally away from the slide. Pin shaft 56 is slidably received in the inclined slot 58 formed in the main wall 62 of switch arm 60. Switch arm 60 is non-flexible and is pivotally mounted on the mounting panel Zil by means of a pin 64; the pivot point is disposed nearer to one end of switch arm 60. At this end, the wall 62 has a horizontally extending tab 66 formed. Secured to the tab 66 and appropriately insulated therefrom by insulation 67 is spring blade 68, which extends horizontally toward the end of switch arm 60 that is farthest from the pivot pin 64. Formed on the free end of spring blade 63 is upwardly facing electrical contact 70. Supported intermediate of the ends of the spring blade 68 on its upper surface is an insulating plate 72. In Fig. 1 it will be observed that the insulating plate is positioned below the bimetal end 36 and the leg 32.

The end of the switch arm 60 farthest from the pivot pin 64 has its lower edge tapered at 74 to provide clearance for some of the other operating parts. On the upper edge of this end is formed a horizontally extending contact mounting plate 76 having downwardly facing contact 78 mounted thereon, and appropriately insulated therefrom by insulation sheets 77' It willbe observed that the contacts 78 and 7t? are positioned adjacent to eachother and are adapted to make and break contact with each other to thereby close or open an electrical circuit which isformed by connecting appropriate electrical wires to appropriate portions of the thermostat and the appliance with which the thermostat is associated The structure described thus far functions in the following manner to control the circuit. By moving the control knob connected to the lever 52, arcuate movement of the lever 52 causes the leverend tomove linearly in ahorizontal plane; this motion is transmitted through thetabs 50 to the slide 49 which moves horizontally one way or the other in slot 38. This horizontal movement is translated by the pin shaft 56 and slot 58 connection into pivotal motion of the switch armotl aboutpine4 due to the incline of the slot. It will thus be seen that by moving the lever 52, the angular position of the ,switcharm 16,0,may be determined and-hence the distancefrom the insulating plate 72 to the bimetal end 36 and the leg 32 may be varied. This constitutes a thermostat adjustment which permits temperature selection, for the distance between the bimetal end 36 and the insulating plate 72 determines the temperature at which the circuit is opened; this obtains because the circuit is opened when the bimetal end 36 deflects downwardly in response .to an increase in temperature until it contacts insulating plate 72 and bends the spring blade 63 clockwise, thereby moving contact 70 away from contact 78. Since the vertical linear distance that thebimetal' end deflects is dependent upon thetemperature, the distance between the bimetal end andinsulating plate 72 determines the temperature which must bereached before the bimetal end will have deflected sulficiently to move the spring blade and partthe contacts.

Theslide may be moved from an ofi position to an infinite number of intermediate temperature settings with- .in the range in which the thermostat will operate. The ofl position is shown in Fig. 5, wherein it will be observed that the slide 40 has beenmoved to the left in the slot 38 almost totheend of the slot. In this position, the switch arm on has been rotated counterclockwise, the insulating plate 72 has contacted the-leg 32 and the spring blade 68 has been deflected downwardly (clockwise) relative tothe remainderof theswitch arm. Thiscausesthc contacts 7 and 78 to part and, therefore, to be maintained in open condition. When set in thismanner, the contacts will not close regardless of the temperaturethence, this constitutes an elf setting.

While some additionalmovement of slide ditto the left appearspossible in Fig. 5, as a practical matter, this view shows the farthest left position of the slide, because other parts of the appliance prevent further movement. For example, the slot in which the lever moves'limits the leftward movement of the lever and hence the slide. This is not a critical aspect of the invention, but is included for the purpose of accuracy, for the-arrangement canbe made such that the ends of slot 38 constitute the limits between which the slide moves.

To 'select any desired temperature, the slide is moved .from the off setting to the right, and the switch arm .60rotates clockwise; after a small arc of rotation, the insulatingplate 72 separates from the leg 32 and returns V to itsnormal position wherein the contacts 70 and'78 are incontact. This constitutesthe lowest temperature setting for which the thermostatwill operate, for it constitutes the shortest distance'betweenfthebimetal end 36 .andthe insulating plate 72 in other thanthe off posii blade 68 downwardly and opens the contacts. It will be understood that when set in this first temperature setting, the circuit is closed and that when the temperature in the vicinity of the bimetal 34 increases, the bimetal end as deflects downwardly. At the predetermined temperature selected, the bimetal end 35 contacts insulating plate 72, bends spring blade 68 clockwise and thereby moves the contact 70 away from the contact 73. in Fig. 4 the parts are shown in position after the bimetal end has deflected and moved the contact 70 away from the contact 7 8. In Fig. ,4 the slide is set at an arbitrary temperature setting whichis the same asthe setting shown in Fig. 1.

From the foregoing it should be apparent that by moving the slide farther to the right from the first setting next to the off position, a higher temperature is selected at which the contacts will be parted, for the distance between the bimetal end and insulating plate is thereby increased. A particularly important feature to be noted is that regardless of the position of the slide and, there fore, of the spring blade 68, that the pressure between the contacts is constant whenever they are in contact. This desirable feature flows from the fact that both contacts are carried by the same member, the switch arm, which is pivotal relative to the bimetal, and that when the thermostat is adjusted, the pressure between the contacts does not vary.

Another important feature to be noted is that when the bimetal deflects to part the contacts, the break is quick, for the wall 62 of the non-flexible'switch arm is maintained fixedly in position and the flexible spring blade 68 is forcibly moved away from the switch arm by the bimetal end 36. In other words, in the illustrated embodiment, by mounting one contact on a nonflexible supporting member which is maintained fixedly, and mounting the other contact on a flexible supporting member that is forced away from the first supporting member, the slow break which results from the prior art devices is eliminated. In prior art device the contacts are mounted on two flexible supporting members; when one member is forced away from the other, the break is slow for the other member follows the one member due to the flexibility of the other member. Therefore, the solution to the problem which I have discoveredis to mount at least one contact on a non-flexible member which is maintained fixedly, and to mount the other contact on another member that is forced away from the non-flexible member when the contacts are parted.

A unitary thermostat has been provided which fulfills each of the objects of this invention. As will be evident from the foregoing description, certain aspects of my invention are not limited to the particular details of construction of the examplesillustrated, and I contemplate that various and other modifications and applications will occur to those skilled in the art.

It is, therefore, my intention that the appendedclaims shall cover such modificationsand applications'as donot depart from the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United-States is:

l. A heat responsive device comprising a casing, a non-flexible switch arm pivotally mounted on said casing, a first electrical contact on said arm, a member secured to said arm and carrying a second electrical contact which is disposed adjacent to said first electrical contact, heatresponsive means for moving and member relative to said arm to shift said second electrical contact from a first position in which it abuts said first contact to a second position in which his spaced from said first contact, and means for pivoting said arm relative to said casing and thereby causing saidmember to move relative-to said heat responsive means for changing the temperature setting of said device.

2. A device as defined in claim 1 wherein said first electrical contact is supported on one end of said arm, and said member comprises a spring blade secured at one of its ends to the other end of said arm, said spring blade supporting said second electrical contact at its free end.

3. A device as defined in claim 1 wherein said heat responsive means comprises a bimetallic strip having one end secured to said casing and its other end bent toward said member.

4. A device as defined in claim 3 wherein said member comprises a spring blade and supports a plate, and said bent end of said bimetallic strip is adapted to deflect in response to a temperature increase into said plate and thereby move said blade and move said second electrical contact from its first position to its second position.

5. A device as defined in claim 1 wherein said pivoting means comprises a linearly movable pin which is slidably mounted in a slot in said switch arm, said slot being inclined at an angle to the line of movement of said pin.

6. A device as defined in claim 5 wherein said pin is secured to a slide which is movably mounted on said casing.

7. A device as defined in claim 6 wherein said slide includes a pair of spaced legs that are adapted to operatively receive an end of a movable lever, whereby movement of said lever causes said slide to move and thereby pivot said switch arm.

8. A device as defined in claim 1 wherein said means for pivoting the switch arm comprises an inclined slot in said switch arm and a horizontally movable pin which is slidably mounted in said slot, whereby horizontal movement of said pin causes said switch arm to pivot.

9. A device as defined in claim 8 wherein said pin is secured to a slide which is mounted on said casing for horizontal movement.

10. A heat responsive control for an electrical circuit comprising a pair of contacts, a casing, a non-flexible switch arm pivotally secured to said casing, one of said contacts carried on an end of said switch arm, a spring blade secured to said arm and carrying the other contact adjacent to said one contact, said blade adapted to normally urge said other contact into engagement with said one contact, a bimetallic strip secured at one of its ends to the casing and having its free end spaced from said blade, and means on said casing for pivoting said arm relative to said casing to thereby alter the space 6 between the free end of said strip and said blade for adjusting the temperature setting, said strip upon being heated adapted to deflect its free end into engagement with said blade and to move said blade, thereby moving said other contact out of engagement with said one contact.

11. A device as defined in claim 10 wherein a stop is positioned adjacent to said blade, said stop being disposed closer to said blade than said free end of said bimetallic strip when said strip is undeflected, said blade adapted to be moved toward and into contact with said stop when said means are moved to a predetermined position, and to thereby permit said one contact to move away from said other contact upon movement of said means past said predetermined position in one direction.

12. A device as defined in claim 11 wherein said one contact is electrically insulated from said switch arm, said blade is electrically insulated from said switch arm, and an insulating plate is secured to said blade in position to be engaged by either said stop or said free end in the event the blade is moved toward said stop sufiiciently or said free end deflects sufiiciently.

13. A device as defined in claim 10 wherein said means comprise a pin which is mounted for linear movement in said casing, and for movement in a slot in said switch arm which is inclined to the line of movement of said pin, whereby movement of said pin causes said switch arm to pivot.

14. A device as defined in claim 1 wherein said means for pivoting said switch arm comprises a slide horizontally mounted on said casing, and a lever movable in a horizontal plane, said slide having a pair of spaced legs that straddle an end of said lever, whereby said legs are free to move vertically relative to said lever end.

15. A device as defined in claim 1 wherein said means for pivoting comprise an elongated slot in said casing, an elongated slot in said switch arm, said slots being disposed at an angle to each other, and a pin slidably mounted in both of said slots, whereby movement of said pin causes said switch arm to pivot.

References Cited in the file of this patent UNITED STATES PATENTS 2,516,502 Altman et al. July 25, 1950 2,622,171 Hiltenbrand Dec. 16, 1952 2,643,311 Giufirida et al June 23, 1953 2,668,889 Baak Feb. 9, 1954 

